One of the principal mechanisms by which cellular regulation is effected is through the transduction of extracellular signals across the membrane that in turn modulate biochemical pathways within the cell. Protein phosphorylation represents one course by which intracellular signals are propagated from molecule to molecule resulting finally in a cellular response. These signal transduction cascades are highly regulated and often overlapping as evidenced by the existence of many protein kinases as well as phosphatases. Phosphorylation of proteins occurs predominantly at serine, threonine, or tyrosine residues and protein kinases have therefore been classified by their specificity of phosphorylation site i.e. serine/threonine kinases and tyrosine kinases. Because phosphorylation is such a ubiquitous process within cells and because cellular phenotypes are largely influenced by the activity of these pathways, it is currently believed that a number of disease states and/or disorders are a result of either aberrant activation or functional mutations in the molecular components of kinase cascades. Consequently, considerable attention has been devoted to the characterization of these proteins.
Akt-1 (also known as PKB alpha and RAC-PK alpha) is a member of the AKT/PKB family of serine/threonine kinases and has been shown to be involved in a diverse set of signaling pathways. Akt-1, like other members of the AKT/PKB family is located in the cytosol of unstimulated cells and translocates to the cell membrane following stimulation. Akt-1 translocation can be activated by several ligands including platelet derived growth factor, epidermal growth factor, basic fibroblast growth factor, cellular stress such as heat shock and hyperosmolarity as well as insulin (Bos, Trends Biochem. Sci., 1995, 20, 441-442) and other studies have shown that this activation is through PI3 kinase which is wortmannin sensitive (Franke et al., Science, 1997, 275, 665-668). Once localized to the plasma membrane, Akt-1 has been shown to mediate several functions within the cell including apoptosis, the metabolic effects of insulin, induction of differentiation and/or proliferation, protein synthesis and stress responses (Alessi and Cohen, Curr. Opin. Genet. Dev., 1998, 8, 55-62; Downward, Curr. Opin. Cell Biol., 1998, 10, 262-267).
Akt-1 was cloned independently in 1991 by three groups (Bellacosa et al., Science, 1991, 254, 274-277; Coffer and Woodgett, Eur. J. Biochem., 1991, 201, 475-481; Jones et al., Cell Regul., 1991, 2, 1001-1009) but its association with primary human gastric carcinoma was recognized as early as 1987 (Staal, Proc. Natl. Acad. Sci. U S A, 1987, 84, 5034-5037). Akt-1 has also been shown to be overexpressed in 3% of breast cancers (Bellacosa et al., Int. J. Cancer, 1995, 64, 280-285).
Akt-1 has been proposed to be a gene involved in chromosomal rearrangement at chromosome band 14q32. This locus is known to undergo rearrangement in human T-cell malignancies such as prolymphocytic leukemias, and mixed lineage childhood leukemias (Staal et al., Genomics, 1988, 2, 96-98).
Akt-1 also plays a role in the prevention of "programmed cell death" or apoptosis. It has been demonstrated that Akt-1 provides a survival signal to cells protecting them from a number of agents including UV radiation (Dudek et al., Science, 1997, 275, 661-665), withdrawal of IGF1 from neuronal cells, detachment from the extracellular matrix, stress and heat shock (Alessi and Cohen, Curr. Opin. Genet. Dev., 1998, 8, 55-62). These findings may explain the overexpression of Akt-1 seen in cancer cells which allows preferential survival of the carcinoma by avoiding the normal progression to apoptosis.
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of Akt-1. Consequently, there remains a long felt need for additional agents capable of effectively inhibiting Akt-1 function.
To date, strategies aimed at inhibiting Akt-1 function have involved the use of various inhibitors of the upstream kinases responsible for phosphorylating Akt-1. However, these strategies are not specific to Akt-1, as many proteins lie upstream of Akt-1 and in several divergent pathways. Antisense oligonucleotides, therefore, provide a promising new pharmaceutical tool for the effective modification of the expression of specific genes including Akt-1.